It may be desirable to operate an engine with greater than 25% of gas mass inducted into a cylinder comprised of recirculated exhaust gas. By operating the engine with higher concentrations of recirculated exhaust gas, it may be possible to increase engine efficiency and reduce the possibility of engine knock. The engine may operate at higher EGR concentrations from lower middle engine loads to higher middle engine loads. At lower engine loads, the engine may operate at lower exhaust gas recirculation (EGR) levels since combustion stability at lower engine loads and higher EGR rates may be less than desired.
During driving from one location to another location, a driver may frequently change engine load responsive to driving conditions such that the engine changes from operating at a lower load to operating at a higher load. Likewise, the driver may change engine load responsive to driving conditions such that engine load changes from a higher load to a lower load. Changes in engine speed and load may result in the fraction of exhaust gas entering engine cylinders to be reduced from a higher concentration to a lower concentration to ensure engine combustion stability. However, response of an engine EGR valve and EGR flow dynamics may cause the fraction of EGR entering engine cylinders to briefly increase when it may be desirable to reduce the fraction of EGR entering engine cylinders. Consequently, the increased fraction of EGR may cause the engine to misfire. If the engine misfires, engine emissions and vehicle drivability may degrade.
The inventors herein have recognized the above-mentioned disadvantages and have developed a method for operating an engine, comprising: inducting a gas mixture into a cylinder, a fraction of the gas mixture comprised of exhaust gas, at least a portion of the gas mixture participating in combustion in the cylinder; and entering the engine into a fuel cut-out state in response to an operating condition change that results in the fraction of the gas mixture changing by more than a threshold percentage.
By entering a fuel cut-out state in response to an operating condition change that results in an exhaust gas fraction of a gas mixture inducted to an engine changing by more than a threshold percentage, the technical result of evacuating excess EGR from an engine intake manifold without the engine misfiring may be possible. For example, if a driver at least partially releases an accelerator pedal resulting in a desired 40% reduction in a fraction of exhaust gas entering the engine, the engine may transition into a fuel cut-out state until a fraction of EGR in the engine's intake manifold is less than a threshold fraction of EGR in the intake manifold. In this way, an engine may be operated with a higher EGR concentration without the engine misfiring when engine load changes.
The present description may provide several advantages. Specifically, the approach may reduce driveline torque disturbances of a hybrid driveline. Further, the approach may improve vehicle drivability. Further still, the approach may reduce driveline wear, thereby increasing the operating life of the driveline.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.